Spectrophotometers are widely used in many settings to determine spectral reflectance. As an industrial quality control tool, spectrophotometers are used to determine whether goods in production are of consistently acceptable appearance. In short, the object is to ensure that the spectral reflectance of the production material is consistent throughout its length and width so that the ultimate goods will be of the highest possible quality. By way of example, textile manufacturers use spectrophotometers during continuous production to monitor the consistency and effectiveness of their dying processes. Ideally, the textile manufacturers would place a spectrophotometer on every final inspection rack to ensure consistent quality of each roll of material at the final production stage prior to shipping. As discussed below, however, limitations of prior spectrophotometers make it impractical for textile manufacturers to mount a spectrophotometer on every inspection rack.
First, previously known spectrophotometers must be mounted in close proximity to the sample being measured, typically within one inch of the production line, in order to eliminate interference from ambient light and obtain a sufficiently intense reflection from the sample. In order to mount prior spectrophotometers in such close proximity to the production material it has been necessary to build expensive bridge mountings which must be custom-designed for each application
Secondly, it is often necessary for the spectrophotometer to be able to scan the continuous production sheet. But prior spectrophotometers must be physically transported across the sample in a spatial scan in order to maintain the spectrophotometer in close proximity to the sample. This type of spatial scanning adds considerably to the cost of the bridge mounts since not only must the spectrophotometer be mounted close to the sample, it must be mounted so that it can move across the sample while maintaining its close position. Needless to say, acceptable tolerances for such a scan are difficult to attain in industrial settings. With respect to the textile industry, textile inspection racks are too numerous for installation of a spectrophotometer on each final inspection rack to be economically feasible. Consequently, textile manufacturers have mounted spectrophotometers only on their dying ranges, which are less numerous than the inspection racks. But measurements made at the dying ranges are a less reliable indication of final product quality than measurements taken at the final inspection stage, so accuracy is plainly sacrificed in order to obtain affordability.
Moreover, the need to movably mount prior spectrophotometers close to the sample and the consequent expense of providing custom bridge mountings have prevented the use of spectrophotometers as a quality control tool in some industries. Indeed, many industries have found installing spectrophotometers too costly due to the cost of the bridge mounts to warrant their use. In addition, the requirement that prior spectrophotometers be situated close to the production line has prevented use of spectrophotometers where the sample environment is simply too harsh for the spectrophotometer or where there is simply insufficient room to install a custom bridge mounting. In other situations the specialized nature of the application makes installation of prior spectrophotometers prohibitive. For example, the food industry has not adopted spectrophotometers as a color measurement tool in part because the bridge mountings would have to be constructed from stainless steel in order to satisfy health standards. The high cost of such mounting structures has to date outweighed the advantages of using spectrophotometers in this industry.
As yet a further drawback, prior spectrophotometers positioned close to the sample surface simply cannot accurately measure some surfaces. Prior spectrophotometers include an illumination source which emits light in many directions from a point source and a detector which receives and detects the light reflected from the surface being measured. This arrangement provides an adequate measurement for most continuous flat surfaces when the light source and detector are placed close to the sample, but is unreliable when surfaces having a relief profile are spatially scanned. By way of example, the manufacture of sculptured carpets is one application where accurate spectral measurements would be desirable but have heretofore been unattainable. These carpets have an uneven surface and a traditional spectrophotometer placed close to such a carpet will not give accurate spectral reflectance measurements since each area of the sculptured carpet reflects light in different directions at varying intensities. Consequently, the light reflected to the detector from a sculptured carpet differs widely from area to area as a result of the carpet contour and a scan of this surface with a traditional spectrophotometer will yield erratic and unreliable results. This limitation is largely responsible for the carpet industry's wholesale refusal to use spectrophotometers since carpet manufacturers are reluctant to adopt a quality control tool which can be used on some but not all of their products.
Therefore, it is one object of the present invention to provide a spectrophotometer which may provide highly accurate spectral measurements when operated from relatively great distances to the subject.
It is a further object of the present invention to provide a spectrophotometer which may be operated at relatively great distances from the subject to obtain an accurate measurement without interference from ambient lighting conditions.
It is yet a further object of the present invention to provide a spectrophotometer which may be operated at relatively great distances to the subject without any need for complex bridge mount constructions.
It is a still further object of the present invention to provide a spectrophotometer which may be operated from a stationary point at a relatively great distance to the subject which provides an accurate scan of the subject.
It is a still further object of the present invention to provide a spectrophotometer which may be operated at relatively great distances to the subject without any need to realign or refocus the spectrophotometer should the distance between the spectrophotometer and the sample change.
It is yet another object of the present invention to provide a spectrophotometer which may be operated at relatively great distances to the sample with the illumination source and the detector arranged adjacent to one another, as in a single housing.
These and other highly desirable and unusual results are accomplished by the present invention in a compact structure which performs a quick, accurate scan to determine the spectral reflectance characteristics of a sample.
Objects and advantages of the invention are set forth in part herein and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the instrumentalities and combinations pointed out in the appended claims.
The invention consists in the novel parts, constructions, arrangements, combinations, steps, and improvements herein shown and described.